The present invention relates to a method and arrangement for feeding fish, as well as to a fodder itself.
Arrangements for breeding fish have been proposed, comprising a fish tank with aerating means and closed devices for purification of water in which fish excrements are deposited and discharged as contaminants. Methods and arrangements have also been proposed where a breeding device is combined with a device for biological purification of water. The latter arrangement comprises a bell-shaped insert which provides for separation of fish excrements from water together with rest of the fish fodder. The disadvantages of the above methods and arrangements are that they result in great loss of the fodder which cannot be avoided during the separation of the fish excrements, and in adversely affecting oxygen content of the water.
Fish fodders have been proposed which are pelletized and comprise protein-containing matters such as fish flour, soy flour yeast, a small quantity of grease and carbohydrates, and also the required salts and vitamins. An additional quantity of yeast are introduced into the fodder in order to improve joining of the amino acids. The above yeast is produced in industrial fermentors on the basis of waist carbohydrates such as, for instance, molasses or whey with high aeration. During this process a great quantity of heat is liberated which must be drawn away by cold water.
It has been recognized that a fish fodder preferably must be held in a certain place so that fish can take the movable fodder, leave the place of feeding and thereafter return to the same place to take a new portion of the fodder.
Fish of prey, such as for instance trout or pike, take a fodder while they swim. This means that the pelletized fodder must swim on a water surface during a certain time. However, the known fodder, which is very expensive, does not swim, but slowly sinks in water is deposited on a bottom of the breeding arrangement and mixed with fish excrements.
Another disadvantage of the known fodder, even in the case where it comprises alginate improving its structural durability, is that the not bonded granules of the fodder are decomposed in water in a few minutes. Even slight movement of water results in rapidly generating of undesirable dirt. Because of the great weight of the thus-produced fodder, it rapidly sinks and is deposited on the bottom of the breeding arrangement. The fodder in the form of dirt cannot be taken by fish, such fodder is lost and increases the quantity of contaminants in the breeding arrangement which must be evacuated from the latter.